This invention relates to a method for controlling the operation of an internal combustion engine at the start of same, and more partiucularly to a method of this kind which is capable of starting the engine in a smooth and stable manner, without spoiling the emission characteristics of the engine.
A fuel injection control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Pat. No. 3,483,851, which is adapted to determine the valve opening period of a fuel injection device for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
According to the above proposed electronic fuel injection control system, when applied to a multi-cylinder engine, a plurality of injectors, which are exclusively provided for the respective cylinders of the engine, are successively actuated in predetermined sequence, in synchronism with generation of pulses of a top-dead-center signal (hereinafter called "the TDC signal"), which are each indicative of a predetermined crank angle of the crankshaft of the engine and are generated in a number equal to the number of the cylinders per cycle of the engine. Determination as to which cylinders the individual pulses of the TDC signal correspond to is made on the basis of the timing of generation of pulses of a cylinder-discriminating signal which are each generated each time the crankshaft rotates through a predetermined angle with respect to a particular cylinder, to thereby carry out fuel injection into the cylinders accurately in predetermined sequence.
However, at the start of the engine, in many cases a first pulse of the above cylinder-discriminating signal is not generated immediately upon starting of the engine, depending upon the angular position of the crankshaft assumed immediately before the start of the engine. In such cases, there can occur a noncoincidence in timing between the suction stroke of a certain cylinder and the valve opening action of the corresponding injector before the first pulse of the cylinder-discriminating signal is generated, so that the supply of fuel into the cylinders is not effected smoothly, preventing smooth and positive starting of the engine.
To eliminate such disadvantage, there has been proposed a method by the assignee of the present application, in which fuel injections are effected into all the cylinders at the same time upon generation of a first pulse of the TDC signal immediately after the start of the engine, thereafter no injection is effected into any of the cylinders until the pistons of all the cylinders have finished their first suction strokes, and after completion of the first suction strokes of all the cylinders, fuel injections are successively effected into the cylinders in predetermined sequence in synchronism with generation of subsequent pulses of the TDC signal (Japanese Patent Provisional Publication No. 57-137626).
However, this proposed method has the weekpoint that when the supply voltage or operating voltage to a central processing unit (hereinafter called "CPU") which forms essential part of electronic control means for carrying out the method can often drop after the start of the engine in cold weather, the CPU is initialized each time the supply voltage recovers its normal level so that concurrent fuel injections into all the cylinders repeatedly take place several times. In other words, in cold starting of the engine, the supply voltage supplied to the CPU from a battery can drop below a lower limit of a range within which the CPU can normally operate, upon closing of a starter switch which, when closed, actuates the starter of the engine which is driven by the same battery. When the supply voltage from the battery drops below the above lower limit, the CPU is reset, and when the supply voltage subsequently recovers a level above the lower limit, the CPU is released from its reset state and initialized. Immediately after actuation of the starter, the supply voltage can repeatedly drop below the lower limit, and accordingly the CPU is initialized repeatedly. A concurrent fuel injection into the all the cylinders takes place upon each initialization of the CPU. As a consequence, an excessive amount of fuel is supplied to the engine, which badly affects not only the operation of the engine but also the emission characteristics and fuel consumption of the engine.